Thermostat for low power circuits



April 5, 1957 R. B. MATTHEWS 2,789,184

THERMOSTAT FOR LOW POWER CIRCUITS Filed July 22, 1955 INVENTOR.

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United States Patent THERMOSTAT FOR LOW POWER CIRCUITS Russell B. Matthews, Wauwatosa, Wis., assignor to Milwaukee Gas Specialty Company, Milwaukee, WlS., a corporation of Wisconsin Application July 22, 1955, Serial No. 523,825

7 Claims. (Cl. 200-140) This invention relates in general to circuit controlling devices and more particularly to thermostats for controlling low power circuits by variation of pressure across electrical contact members which are continuously in contact with one another during the operative cycle of the thermostat, said variation in pressure being etfectuated by changes in temperature.

It is a general object of the present invention to provide a thermostat of the aforementioned general characteristics which employs magnetic actuating members one of which has magnetic characteristics which vary continuously and substantially with temperature changes.

Another object of the present invention is to provide a device of the aforementioned character having embodied therein a pair of enclosed or encapsulated contacts in physical or mechanical engagement throughout the operative control cycle of the device, the amount of force or contact pressure on said contacts varying inversely with changes in temperature as a result of a change in permeability in one of the magnetic actuating members in response to said temperature changes.

Still another object of the present invention is to provide the device as outlined above with magnetic members which are linked by the flux produced by a flux producing means, the amount of flux produced thereby being substantially constant, and the variable pressure on the contacts being caused solely by a substantially linear variation of the permeability of one of the magnetic members per degree temperature change.

A more specific object of the present invention is to provide an expansible and contractible enclosure tending to bias the enclosed low and variable resistance contacts out of engagement, said enclosure being hermetically sealed and filled with an inert fill to protect said contacts against corrosion, foreign matter and films deleterious to maintenance of constant pressure-resistance characteristics at said contacts.

Still another object of the present invention is to provide a device of the aforementioned type having a permanent magnet operator enclosed within a metallic enclosure, said enclosure having an end wall of variable permeability for coaction with said permanent magnet.

Another object of the present invention is to disclose a new method of effecting a controlling change in the current flow from a thermoelectric generator through low resistance contacts which are normally in mechanical engagement throughout the control cycle, by changing the permeability of at least one of a pair of magnetic contact actuating members to effect a predetermined change in the contact resistance of said contacts and thereby a controlling change in said thermoelectric current flow.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be 2,789,184 Patented Apr. 16, 1957 understood by the following description of specific embodiments when read in connection with the accompanying drawing, in which:

Figure l is a sectional view of one embodiment of the invention connected in circuit with a thermoelectric generator and a valve which are shown semi-diagrammatically; and

Figure 2 is a sectional view of a modified form of the invention.

While the invention may take a number of forms, the thermostatic control device system selected for illustration in Figure l of the drawing comprises a thermostat 13 which may be connected in circuit with a source of small electric power, for example the thermoelectric generator 11, and with an electroresponsive valve 12 or other similar apparatus.

More specifically the thermostat 13 comprises an expansible and contractible enclosure which may take the form of a metallic bellows 14 having a flexible side wall 15 provided with a centrally depressed movable end wall 18 integral therewith. The flexible side wall 15 biases the movable end wall 18 in an outwardly or expanding direction. At its opposite end the bellows 14 has a fixed end wall 20 formed with an axial tubular inwardly extending portion 20:: and an annular axially offset peripheral flange 20b which extends radially beyond the side wall 15. The flange portion 20b is adapted to be fixedly connected to a temperature communicating surface, for example a Wall of a water heater, the bonnet of a furnace, or the like.

The tubular portion or extent 20a defines an axial opening 19 for receipt of the flanged sleeve 25 of a glass or other suitable seal 28 which seals the opening 19. A conductor stem 23 extends into the interior of the bellows 14 through the seal 28 and terminates in a contact 24 constituting the fixed contact of the thermostat.

At the opposite end of the bellows, a tubular clamping member 26 forming part of a glass or other suitable seal 30, extends sealingly inwardly through an axial opening 17 in the end wall 18. One end of the member 26 may be flanged, as shown, and sealingly fixed, as by soldering, to the outer surface of end wall 13. The member 26 extends through a bore therefor in a magnet operator 32, to be described in greater detail later herein, and other end of the member 26 is flanged to clampingly engage the operator 32 as shown. A contact stem 22 extends into the interior of the bellows through the seal 28 and terminates in a contact 21 cooperable with the contact 24 and constituting the relatively -movable contact of the device. The outer end of contact stem 22 is connected in circuit, through suitable conductors such as 22a, to one terminal of the thermoelectric generator 11. The contact stem 23 is connected in circuit with one terminal of the valve 12 through a conductor 23a. The series circuit is completed by a conductor 41 connecting the other terminal of the generator 11 in circuit with the other terminal of the valve 12.

While the contact 21 is movable with respect to contact 24 it is preferred to keep the contacts 21 and 24 in engagement at all times during the control cycle of the device, control being effectuated by variation of the contact pressure. The contacts are preferably made of low resistance material, for example silver.

The contact actuating means for the improved thermostat includes flux generating means which may take the form of the generally U-shaped permanent magnet operator 32 fixedly clamped to the movable end wall 18 within the bellows 14 by the inner flanged portion of the tubular clamping member 26. It is, of course, obvious that an electromagnet may be substituted for the permanent magnet 32 if desired. The two legs of the 7 meability per degree temperature change and of affording a low range of Curie points. These alloys are available commercially, and it is preferable to use alloys with a nickel content of 28.5 to 32.5%. For controlling a house furnace in the normal room temperature range it is preferred to use as the material for the end wall 20 an ironnickel alloy having approximately 30% nickel. The magnet 32 preferably generates sufiicient flux to provide an attractive force biasing the magnet 32 toward the wall 20 and thereby the contact 21 toward the contact 24 with sufiicient force to permit suflicient thermoelectric current to now for actuation of the valve 12 when the end wall is at approximately 50% of its maximum permeability. A decrease in the permeability of the wall 20, of course, reduces the aforementioned attractive force and contact pressure and increases the contact resistance to a point preventing the flow of sufficient thermoelectric current to hold the valve 12 open, whereupon said valve closes.

The bellows 1 4 may be filled with fill which is inert with respect to the contacts and which will not aifect the spring rate of the bellows 14. One such fill is nitrogen, and it is apparent that in order to contain the fill, it is preferable to have the bellows 14 hermetically sealed.

Adjustment of the temperature control point of the improved thermostat may be provided by suitable adjustable biasing means such as a loading spring 40 which is interposed between the cup-shaped depression of end Wall 18 and a pressure plate 38. A cup-shaped protective housing 16 surrounds the bellows 14 and is fixed to the peripheral flange portion 20b of the wall 20. An adjustment screw 36 is threaded through the outer wall of the casing 16 and engages the pressure plate 38 The amount of loading of the bellows may be varied by turning the screw 36 to thereby vary the temperature at which the contacts will cycle the valve 12.

It is to be noted that the invention contemplates no substantial movement of the magnet 32 toward and away from the armature end wall 20 during the control cycle. Rather, the change in permeability of the temperature sensitive material effectuates direct changes in the mechanical pressure on the contacts 21 and 24 as distinguished from relative separation and engagement of the contacts. Thus, the spring rate of the flexible wall of the bellows serves merely to provide loading and is pref erably relatively light as compared to the attractive force of the magnet 32.

Figure 2 illustrates another form of the invention wherein the elements indicated by primed reference characters correspond to similar parts in Figure 1 indicated by unprimed reference characters. In Figure 2 the end Wall need not be magnetically permeable, and an annular ring 50 is fixed to the inner surface thereof for coaction with the magnet 32. The ring 50 is made of the same temperature sensitive, variable permeability metal as the wall 20 in the form of the invention shown in Figure 1, and the control device shown in Figure 2 operates in substantially the same manner as that shown in Figure 1.

Although specific embodiments of the invention have been shown and described, it is with full awareness that many modifications thereof are possible. The invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

What is claimed as the invention is:

1. A control device for low power circuits comprising low resistance cooperating contacts normally in engage- 4. ment throughout the operative control cycle of said device, biasing means biasing said contacts toward disengagement, actuating means operatively associated with said contacts for biasing the latter into engagement and providing a variable contact pressure to thereby vary the contact resistance of said contacts, said means comprising flux producing means including a first magnetic member, and a second magnetic member positioned in coacting relationship with said flux producing means to produce an actuating force therebetween, one of said members being of material the permeability of which varies. with changes in temperature, whereby at one temperature the actuating force between said magnetic members provides suilicient contact pressure to afford a contact resistance of a value permitting the flow of a predetermined small electric current therethrough, and whereby on a predetermined change in temperature the permeability of said one magnetic member, and hence the actuating force between said magnetic members, changes to thereby reduce the contact pressure sufficiently to increase the contact re slstance to a value preventing the flow of said predetermined small electric current therethrough.

2. A control device for thermoelectric circuits comprising a pair of enclosed low resistance cooperating contacts normally in engagement throughout the operative control cycle of said device, biasing means biasing said contacts toward disengagement, actuating means op eratively associated with said contacts for biasing the latter into engagement and providing a variable contact pressure to thereby vary the contact resistance of said contacts, said means comprising flux producing means including a first magnetic member, and a second magnetic member positioned in coacting relationship with the flux producing means to produce an actuating force there-- between, one of said members being of material the. permeability of which varies inversely with changes in temperature, whereby at one temperature the actuating force between said magnetic members provides sutlicient contact pressure to afford a contact resistance of a value permitting the flow of a predetermined small current therethrough, and whereby on a predetermined change in tem perature the permeability of said one magnetic'member, and hence the actuating force betweensaid magnetic members, changes to thereby reduce the contact pressure sufiiciently to increase the contact resistance to a 'value preventing the flow of said predetermined small current therethrough.

3. A thermostat for low power circuits comprising low resistance cooperating contacs biased toward disengagement, enclosure and actuating means for said contacts, said means comprising flux producing means including a first magnetic member, and a second'magnetic member positioned in coacting relationship with said first member to produce an actuating force therebetween biasing said contacts into engagement throughout the operative con-- trol cycle of said device, said second member being of material the permeability of which varies with changes intemperature to vary the actuating force between saidmagnetic members, whereby at one temperature the actuating force between said magnetic members provides sufficient contact pressure to afio'rd a contact resistance of a value permitting the flow of a predetermined small electric current therethrough, and whereby on a predetermined change in temperature the actuating force between said magnetic members affords a contact pressure reduced sufficiently to increase the contact resistance to a value preventing the flow of said predetermined small electric current therethrough.

4. A control device for low power circuits comprising an hermetically sealed expansible and contractible'e nclosure having an inert fill, a pair of pressure responsive low and variable resistance solid contacts biasedv towarddisengagement and encapsulated within said encl ure, said contacts being normally in engagement throughout the operative control cycle of said device, means for exerting a variable compression force on said contacts to vary the contact resistance therebetween, comprising a permanent magnet and a magnetic member positioned to be linked by the flux produced by said magnet for attraction thereto, said member being of a material the permeability of which varies with changes in temperature, whereby at one temperature the permeability of said one member is of a level to afford a predetermined attractive relationship between said magnet and member providing a contact resistance sufficiently low to permit a predetertermined low power current to flow therethrough, and whereby at a predetermined different temperature the permeability of said member is of a different level to reduce the attractive relationship between said magnet and member and thereby effect a predetermined higher resistance between said contacts preventing said predetermined low power current from flowing therethrough.

5. A thermostat for low power circuits comprising an expansible and contractible hermetically sealed enclosure biased to an expanded position, a metallic end wall of said enclosure made of material the permeability of which varies inversely with changes in temperature, a pair of normally mechanically engaged pressure responsive low and variable resistance contacts Within and relatively movable with the expansion and contraction of said enclosure, magnetic actuating means tending to contract said enclosure and including flux producing mean operatively associated with said end wall to provide a variable contactile force on said enclosure in opposition to said bias, said variable contractile force efiectuating corresponding changes in the contact pressure on said contacts to thereby effect inverse changes in the contact resistance between said contacts, whereby at one predetermined temperature the permeability of said end wall is of a level to permit the magnetic flux of said flux producing means to provide a first contractile force on said enclosure sulficient to afford a contact resistance of a level permitting a predetermined small electric current to flow therethrough, and whereby at a predetermined different temperature the permeability of said end wall is of a substantially different level to provide a reduced contractile force on said enclosure and reduced contact pressure to thereby increase the contact resistance to a level preventing the flow of said predetermined small electric current therethrough.

6. A thermostat for low power circuits comprising an expansible and contractible hermetically sealed enclosure having a pair of end walls biased to an expanded position, a pair of normally mechanically engaged pressure responsive low and variable resistance contacts fixed to said end walls within and relatively movable with the expansion and contraction of said enclosure, one of said end walls being made of a material the permeability of which varies with changes in temperature, magnetic actuating means for said enclosure including a permanent magnet fixed to the other end wall within said enclosure, said permanent magnet being operatively associated with said permeable end wall to provide a variable contractile force on said enclosure in opposition to said bias, said variable contractile force effectuating corresponding changes in the contact pressure to thereby effect inverse changes in the contact resistance, whereby at one predetermined temperature the permeability of said end wall is of a level to permit the magnetic flux of said magnet to provide a first contractile force on said enclosure suificient to afford a contact resitance of a level permitting a predetermined small electric current to flow therethrough, and whereby at a predetermined higher temperature the permeability of said end wall is of a substantially different level to thereby provide a reduced contractile force on said enclosure and reduced contact pressure to thereby increase the contact resistance to a level preventing the flow of said predetermined small electric current therethrough.

7. The method of effecting a controlling change in the current flow in a low power circuit connected to a source of small electric energy and including low resistance contacts having actuating means including coacting magnetic members normally biasing said contacts into engagement, comprising changing the permeability of at least one of said magnetic members to effect a predetermined change in said biasing force and thereby a change in the resistance between said contacts suificient to effect a controlling change in the current flow in said circuit while retaining said contacts in engagement.

References Cited in the file of this patent UNITED STATES PATENTS 822,323 Thomson June 5, 1906 2,195,633 Rohr Apr. 2, 1940 2,717,123 Hilgert et al. Sept. 6, 1955 2,718,569 Johnston Sept. 20, 1955 

